Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $181.86   11.838%   $203.3886   $203.39   $203.40   $203.40  
  Purchase #2 $245.57   11.140%   $272.9265   $272.93   $272.95   $272.90  
  Purchase #3 $225.68   9.171%   $246.3771   $246.38   $246.40   $246.40  
  Purchase #4 $96.67   3.605%   $100.155   $100.16   $100.15   $100.20  
  Purchase #5 $174.78   10.593%   $193.2944   $193.29   $193.30   $193.30  
  Purchase #6 $249.58   7.558%   $268.4433   $268.44   $268.45   $268.40  
  Purchase #7 $183.52   8.591%   $199.2862   $199.29   $199.30   $199.30  
  7 purchase totals = $1,357.66       $1,483.8711   $1,483.88   $1,483.95   $1,483.90